There is a need for core sampling in geological surveying operations.
Core samples are obtained through core drilling operations. Core drilling is typically conducted with a core drill comprising outer and inner tube assemblies. A cutting head is attached to the outer tube assembly, so that rotational torque applied to the outer tube assembly is transmitted to the cutting head. A core is generated during the drilling operation, with the core progressively extending along the inner tube assembly as drilling progresses. When a core sample is acquired, the core within the inner tube assembly is fractured. The inner tube assembly and the fractured core sample contained therein, are then retrieved from within the drill hole, typically by way of a retrieval cable lowered down the drill hole. Once the inner tube assembly has been brought to ground surface, the core sample can be removed and subjected to the necessary analysis.
Typically, the core drilling operation is performed at an angle to the vertical, and it is desirable for analysis purposes to have an indication of the orientation of the core sample relative to the ground from which it was extracted. It is therefore important that there be some means of identifying the orientation the core sample had within the ground prior to it having been brought to the surface.
Core orientation devices are used to provide an indication of the orientation of the core sample.
One common way of obtaining an indication of the orientation of a core sample is through use of an orientation spear comprising a marker (such as a crayon) projecting from one end of a thin steel shank, the other end of which is attached to a wire line.
The orientation spear is lowered down the drill hole, prior to the inner tube assembly being introduced. The marker on the orientation spear strikes the facing surface of material from which the core is to be generated, leaving a mark thereon. Because of gravity, the mark is on the lower side of the drill hole. The inner tube assembly is then introduced into the outer tube assembly in the drill hole. As drilling proceeds, a core sample is generated within the inner tube assembly. The core sample so generated carries the mark which was previously applied. Upon completion of the core drilling run and retrieval of the core sample, the mark provides an indication of the orientation of the core sample at the time it was in the ground.
There are also mechanical core orientation devices for marking a core sample prior to its extraction from the drill hole. Typically, mechanical devices are adapted to be incorporated in the inner tube assembly for marking the core. An example of such a mechanical orientation device is disclosed in WO 03/038212.
It is against this background and the problems and difficulties associated therewith that the present invention has been developed.